In a central air conditioning system providing cooling, there are at least two fluid circuits. One circuit is the closed circuit in which the refrigerant is compressed, condensed and expanded. The second circuit is where conditioned air is supplied to the zone(s) and subsequently withdrawn to be re-cooled. A third fluid circuit would exist where chilled water is circulated to fan coil units to provide cooling to the air passing through/over the coils and the water is subsequently returned to the chiller of the air conditioning system to be re-cooled. The air conditioning system and fan coil units are very compact relative to the volumes for which they provide cooling.
Conditioned air is delivered by fans or blowers into ductwork and passes via terminals into zones/rooms. The conditioned air will typically be dehumidified when the system is in the cooling mode. The air supplied to a zone cannot be too cool or at too rapid a velocity as to cause drafts which would cause discomfort to the occupants of the zone. Accordingly, large volumes of air are required at relatively low velocities. As a specific example, cooling air is typically supplied at 55xc2x0 F. for a zone made up of a manufacturing space with a cooling load of 300 tons (3,600,000 Btu/hr). Assuming that the conditioned air is warmed from 55xc2x0 F. to 70xc2x0 F. before being withdrawn, 220,000 standard cfm of air would have to be supplied to the zone. The ductwork to the most remote zone could extend for 400 feet and the velocity could be as much as 5000 ft./min. in the case of a manufacturing space with a high velocity air transmission system. This high velocity, however, is an extreme value and would be in the main line prior to branching with the additional total flow cross section, flow losses in the ducts, and the diffusing function of the terminals relative to the flow due to their increased flow cross section.
For a three hundred ton refrigeration system, the refrigerant charge would be on the order of 600 pounds. Due to an affinity between refrigerants and lubricants, some lubricant would be present in the refrigerant. In the closed circuit, gaseous refrigerant is drawn into the compressor where the refrigerant would be compressed to 131 psia and 120xc2x0 F. and would flow at a rate of 360 cubic feet/minute into an six inch diameter path made up of two legs totaling four feet with a 90 xc2x0 elbow therebetween which define the discharge line. The hot, high pressure gas flows from the discharge line into the condenser. In the condenser the gaseous refrigerant condenses as it gives up heat due to heat transfer via a water cooled heat exchanger. The condensed refrigerant which is at 95xc2x0 F. and 131 psia is discharged via a two inch line, eight feet in length. The condensed refrigerant then passes through an expansion device which requires the condensed refrigerant to pass through a restriction thereby undergoing a pressure drop and partially flashing as it passes into the evaporator/chiller. In the evaporator the remaining refrigerant evaporates due to heat transfer via a water cooled heat exchanger. The water gives up heat to the refrigerant and the cooled water is supplied to fan coil units where air passes over/through the coils and is cooled and supplied to the ductwork for delivery to the zones to provide cooling. The gaseous refrigerant in the evaporator is at 45xc2x0 F. and 54 psia and is then supplied via the suction line which is eight inches in diameter with two legs totaling three feet with a 90xc2x0 elbow therein. The flow through the suction line to the compressor completes the cycle.
In comparing the gaseous flows in the two circuits it will be noted that the supply and return air flows can each be on the order of one hundred feet in length with a number of turns and branches with a maximum flow cross section, for each branch, on the order of four square feet and a maximum supply velocity on the order of eighty three feet per second as an extreme value in the main line prior to branching, etc. For the gaseous refrigerant the discharge line is six inches in diameter and four feet in length with a 90xc2x0 bend and the gas is at 131 psia, 120xc2x0 F. and traveling at a velocity of 31 feet/sec. The suction line is eight inches in diameter and three feet in length with a 90xc2x0 bend and the gas is at 45xc2x0 F. and 54 psia and traveling at a velocity of 37.8 feet/sec. The suction and discharge flows are pulsed due to the compression process so the velocities are averages.
Due to long flow paths and the need to minimize pressure losses it is common to use turning vanes in air ductwork systems.
The gaseous refrigerant flow, although having a short flow path, must make at least one 90xc2x0 turn which produces flow losses. The flow into a condenser of the shell and tube type is typically perpendicular to the tube direction and the tubes are simply supported. The refrigerant condenses on the outside of tubes carrying water which takes the heat out of the refrigerant gas. Therefore, it is common practice to place a plate between the discharge flow and the condenser tubes to prevent direct impingement of the discharge gas on the tubes which can cause the tubes to vibrate and fatigue. The present invention locates turning vanes in the elbows of the suction and discharge lines thereby reducing flow losses by reducing secondary flow losses by guiding the flow through the elbows. Additionally, turning vanes are located at the entrance to the condenser. These vanes are located at an otherwise straight flow into the protective plate at the entrance to the condenser and provide a back pressure to reduce the pressure drop in the discharge line. These turning vanes also act like terminals in distributing the flow relative to the heat exchanger structure in the condenser.
It is an object of this invention to minimize pressure drops in the fluid lines of a refrigerant circuit.
It is another object of this invention to increase chiller efficiency.
It is a further object of this invention to reduce the pressure drop in a compressor discharge. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.
Basically, turning vanes are located in the suction and discharge line elbows of a refrigerant circuit and at the entrance to the condenser.